I. Field of the Invention
This invention relates to a spark plug for use in internal combusion engines, and more particularly for modern internal engines which can perform efficiently for extended periods, such as 100,000 miles between tune ups.
II. Description of Prior Art
Both diesel engines and gasoline engines work on the principle of internal combustion. The energy created by combustion (burning of fuel) is converted into mechanical energy. In the case of a diesel engine, air is taken into the cylinder and heavily compressed. The air reaches about 1000 degrees F. (538 degrees C.), so when fuel is sprayed into the cylinder it ignites (catches fire). The explosion forces the piston to move.
In a gasoline engine, however, a mixture of fuel and air is taken into the cylinder at a lower compression and temperature. The mixture must be ignited by an electric spark from a plug inserted in the cylinder, and this explosion forces the piston to move and so turn the crankshaft.
When the engine is running, a pulse of electrical energy at a very high voltage is passed to the terminal of the plug. Car engines, of course, have several cylinders, and in this case the distributor passes the electrical pulses to each of the spark plugs in turn.
The center of this conventional spark plug is an electrode which is imbedded in a ceramic insulator. Separated from the end of the electrode center by a narrow gap is another electrode which is grounded to the cylinder block of the engine. The electrical pulse makes a spark jump across the gap between the center electrode and the grounded electrode.
Designs of spark plugs vary considerably. A typical plug has a body made of steel plated with zinc for protection. The screw threads are precisely rolled to international standards. The insulators are made from a rough ceramic material of fired aluminum oxide. The electrodes are normally made from nickel alloys. A gas tight seal made from aluminum oxide powder is placed between the center electrode and the insulator, and also between the insulator and the plug body.
The conventional plug consists essentially of two (2) electrodes, the insulator, containing a central electrode, and the body with its screw thread and earth electrode that extends from the end of the body into near contact with the lower tip of the central electrode. The ignition current coming from the distributor flows through the central electrode and produces the spark between the central electrode and the earth electrode. The ignition voltage, prior to electronic ignitions was about 25,000 volts. With the advent of modern ignition systems, the voltages have risen, depending upon the application, by a multiple of 2 or 3 times those earlier voltages. And with the greatly increased voltage the wear upon electrodes of conventional spark plugs in turn is greatly increased. The optimal gap between electrodes is altered by the increased wear and the plugs must be changed at a greater rate. With conventional spark plugs as a result of use, the sharp corners of the center electrode and the grounding electrode become rounded. This increases the voltage required to fire the plug which can lead to hard starting and misfiring under load.
In order to increase the life of spark plugs, newer, exotic, and more expensive materials have been used in the manufacture of spark plugs both to disperse the heat generated by the higher voltages and to resist pitting and other forms of physical deterioration of the electrodes. An example that incorporates exotic metals is U.S. Pat. No. 3,958,144. Other recent spark plug inventions which profess to increase spark plug life are the three (3) earth electrode design of U.S. Pat. No. 5,189,333, and the split prong designs of U.S. Pat. Nos. 5,264,754 and 4,916,354. U.S. Pat. No. 5,280,214 discloses a spark plug which utilizes an annular ground electrode to give increased spark between the ground electrode and the center electrode. The prior art does not teach the structure or advantages of the spark plug of the present invention described herein.